When you are dealing with company stock, often the Form 1099-B will not state the correct cost basis for shares sold so you need to enter an adjusted cost basis. You will see an option for that on the screen where you enter the stock sale in TurboTax:

Once you indicate that the cost basis is incorrect or missing on your 1099-B form, you can then enter the correct cost basis. You will typically see the income from the discount on the acquisition of the stock listed on your W-2 form, in box 12 or 14. You can take that amount plus any additional amount you paid for the stock and divide it by the number of shares acquired to determine the cost per share. You can multiply that by the number of shares sold to arrive at the cost basis to report for the sale of the shares. You will also see an option to allow TurboTax to help you determine the correct cost basis.
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